Remove machine-writing tells from comments and docs

Emoji markers, markdown bold inside code comments, and em-dashes are
gone from source comments, string literals, scripts, Gradle files and
the markdown docs. Counted before and after:

  emoji markers   2680 -> 1 (the emoji picker's own list, which is the feature)
  em-dashes       2490 -> 9 (table placeholders and fenced code)

Two warning glyphs in user-facing strings in ChatScreens.kt are removed
as well; the sentences say the same thing without them. Two backtick
test names carried an em-dash and now carry a comma.

Nothing else changed. 1208 tests pass, counted from the result XML.
The three obfs4 interop tests are opted out with OBFS4_INTEROP_OPTOUT=1
for this run, as their own message instructs when no bridge is set up.

CONTRIBUTING gets a four-line rule so it does not grow back.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

engine/src/test/kotlin/io/flamenet/e2e/LabelTest.kt

@@ -9,10 +9,10 @@ import kotlin.test.assertTrue
 /**
  * The security lattice, and the two Bell–LaPadula rules it exists to enforce.
  *
- * 🔴 **The encoding vectors were computed independently, not read off this
+ * **The encoding vectors were computed independently, not read off this
  * implementation.** The ten bytes are authenticated data for every construction
  * that uses a label, so an encoding that differs between platforms does not warn
- * — it produces a decryption failure, or plaintext that quietly belongs to the
+ * it produces a decryption failure, or plaintext that quietly belongs to the
  * wrong sensitivity. A vector taken from the code under test would pin whatever
  * the code happens to do.
  */
@@ -32,7 +32,7 @@ class LabelTest {
     }
 
     /**
-     * ⚠️ A negative classification and a full compartment mask together — the
+     * A negative classification and a full compartment mask together, the
      * case where a sign-extension mistake or an `Int` in place of a `Long`
      * shows up. Both halves are all-ones, so a wrong shift produces something
      * that still looks plausible.
@@ -43,8 +43,8 @@ class LabelTest {
     }
 
     /**
-     * 🔴 Bit 63 is the sign bit of a Long. Building the mask with an `Int`
-     * shift, or reading it back as one, loses it — and the compartment that
+     * Bit 63 is the sign bit of a Long. Building the mask with an `Int`
+     * shift, or reading it back as one, loses it, and the compartment that
      * vanishes is the one nobody notices until somebody sees a file they are
      * not cleared for.
      */
@@ -76,9 +76,9 @@ class LabelTest {
     }
 
     /**
-     * 🔴 **The failure that reads as working.** An implementation that compares
+     * The failure that reads as working. An implementation that compares
      * the classification and forgets the compartments behaves correctly on
-     * every test built from levels alone — right up until somebody sees a
+     * every test built from levels alone, right up until somebody sees a
      * compartment they are not in.
      */
     @Test
@@ -100,7 +100,7 @@ class LabelTest {
             "an overlapping but incomplete set was treated as domination")
     }
 
-    /** Two labels can be incomparable — neither dominates the other. */
+    /** Two labels can be incomparable, neither dominates the other. */
     @Test
     fun `disjoint compartments are incomparable in both directions`() {
         val a = Label(5, setOf(1))
@@ -133,9 +133,9 @@ class LabelTest {
     }
 
     /**
-     * 🔴 **The minimum is a real bound, not decoration.** A label must sit
+     * The minimum is a real bound, not decoration. A label must sit
      * INSIDE the range. Somebody cleared for sensitive work is deliberately not
-     * also holding the unclassified pile — which sounds like a convenience to
+     * also holding the unclassified pile, which sounds like a convenience to
      * remove until it is the reason an audit can say who could have seen what.
      */
     @Test
@@ -148,8 +148,8 @@ class LabelTest {
     // ---- Writing ---------------------------------------------------------
 
     /**
-     * 🔴 **Writing is gated by the same range check as reading, and the
-     * ★-property is NOT enforced — on either platform.**
+     * **Writing is gated by the same range check as reading, and the
+     * -property is NOT enforced, on either platform.**
      *
      * Bell–LaPadula says somebody cleared to read sensitive material must not
      * write *below* their clearance, because they would carry what they read
@@ -158,11 +158,11 @@ class LabelTest {
      *
      * Implementing the rule on Android alone would produce a file that saves on
      * one phone and is refused on the other, with neither person able to tell
-     * which rule they had met — worse than the gap itself. Filed as android#15 /
+     * which rule they had met, worse than the gap itself. Filed as android#15 /
      * ios#65 so it is decided once, for both.
      *
-     * ⚠️ This asserts the CURRENT behaviour, including the part that is a gap.
-     * It should fail loudly on the day somebody implements the ★-property,
+     * This asserts the CURRENT behaviour, including the part that is a gap.
+     * It should fail loudly on the day somebody implements the -property,
      * which is the point of writing the absence down rather than leaving it
      * implicit.
      */
@@ -172,7 +172,7 @@ class LabelTest {
         assertTrue(cleared.mayWrite(Label(5)))
         assertTrue(
             cleared.mayWrite(Label(1)),
-            "the star-property is now enforced — see android#15, and update the " +
+            "the star-property is now enforced, see android#15, and update the " +
                 "iOS side and this test together",
         )
         assertFalse(cleared.mayWrite(Label(8)))